Hypertrophic cardiomyopathy (HCM) is a major cause of sudden death in young adults. Most cases are believed to be the result of an autosomal dominant inherited trait. Salient features of the cardiac pathology include increased muscle mass with fiber disorganization and myofibrillar disarray of the affected myocardium which consistently involves the interventricular septum. The free ventricular wall may also be involved in up to 30% of cases. This project seeks to characterize the defective cellular structures, their proteins and genes involved in the disarray and disorganization of the myocardium in familial cases of HCM. Biopsy material from the left septum and left ventricular free wall will be obtained from catheterization of HCM patients with documented familial occurrence, non-HCM cardiac patients, and from explanted hearts of non-HCM patients with a spectrum of cardiomyopathies. Myofibrils and Z-discs will be prepared from glycerinated myocardial fibers. Immunocytochemistry of membrane-cytoskeletal proteins including alpha-actinin, desmin, spectrin and sarcoplasmic reticulum Ca++-ATPase will be performed in order to determine the subcellular location of the defect. One- and two-dimensional electrophoresis and immunoblotting of proteins from myofibrillar and non- myofibrillar fractions and from Z-disc and 0.6 M KI-extractable fractions will be analyzed for alterations in molecular weight, change, and content. Specific antibodies will be used to screen a lambda gt11 expression library of human cardiac cDNAs, if the gene for the altered protein or closely related isoform is not already cloned or sequenced. The cloned gene or synthetic oligonucleotide will be used in concurrent genomic studies to uncover the DNA sequence alteration. The antibody and DNA probes will ultimately be used to study the pathogenesis of myocardial disarray and dysfunction in familial HCM.